Date: Mon, 12 Nov 2012 22:04:23 -0800 From: Alfred Perlstein <bright@mu.org> To: Andre Oppermann <oppermann@networx.ch> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Peter Wemm <peter@wemm.org> Subject: Re: auto tuning tcp Message-ID: <50A1E2E7.3090705@mu.org> In-Reply-To: <50A14460.9020504@mu.org> References: <50A0A0EF.3020109@mu.org> <50A0A502.1030306@networx.ch> <50A0B8DA.9090409@mu.org> <50A0C0F4.8010706@networx.ch> <EB2C22B5-C18D-4AC2-8694-C5C0D96C07B3@mu.org> <50A13961.1030909@networx.ch> <50A14460.9020504@mu.org>
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On 11/12/12 10:48 AM, Alfred Perlstein wrote:
> On 11/12/12 10:01 AM, Andre Oppermann wrote:
>>
>> I've already added the tunable "kern.maxmbufmem" which is in pages.
>> That's probably not very convenient to work with. I can change it
>> to a percentage of phymem/kva. Would that make you happy?
>>
>
> It really makes sense to have the hash table be some relation to
> sockets rather than buffers.
>
> If you are hashing "foo-objects" you want the hash to be some relation
> to the max amount of "foo-objects" you'll see, not backwards derived
> from the number of "bar-objects" that "foo-objects" contain, right?
>
> Because we are hashing the sockets, right? not clusters.
>
> Maybe I'm wrong? I'm open to ideas.
Hey Andre, the following patch is what I was thinking
(uncompiled/untested), it basically rounds up the maxsockets to a power
of 2 and replaces the default 512 tcb hashsize.
It might make sense to make the auto-tuning default to a minimum of 512.
There are a number of other hashes with static sizes that could make use
of this logic provided it's not upside-down.
Any thoughts on this?
Tune the tcp pcb hash based on maxsockets.
Be more forgiving of poorly chosen tunables by finding a closer power
of two rather than clamping down to 512.
Index: tcp_subr.c
===================================================================
--- tcp_subr.c (revision 242936)
+++ tcp_subr.c (working copy)
@@ -235,7 +235,7 @@
* variable net.inet.tcp.tcbhashsize
*/
#ifndef TCBHASHSIZE
-#define TCBHASHSIZE 512
+#define TCBHASHSIZE 0
#endif
/*
@@ -282,6 +282,27 @@
return (0);
}
+/*
+ * Take a value and get the next power of 2 that doesn't overflow.
+ * Used to size the tcp_inpcb hash buckets.
+ */
+static int
+maketcp_hashsize(int size)
+{
+ int hashsize;
+
+ /*
+ * auto tune.
+ * get the next power of 2 higher than maxsockets.
+ */
+ hashsize = 1 << fls(maxsockets);
+ /* catch overflow, and just go one power of 2 smaller */
+ if (hashsize < maxsockets) {
+ hashsize = 1 << (fls(maxsockets) - 1);
+ }
+ return hashsize;
+}
+
void
tcp_init(void)
{
@@ -296,9 +317,20 @@
hashsize = TCBHASHSIZE;
TUNABLE_INT_FETCH("net.inet.tcp.tcbhashsize", &hashsize);
+ if (hashsize == 0) {
+ /* auto tune based on maxsockets */
+ hashsize = maketcp_hashsize(maxsockets);
+ }
+ /*
+ * Be forgiving of admins that don't know to make the tunable
+ * a power of two.
+ */
if (!powerof2(hashsize)) {
- printf("WARNING: TCB hash size not a power of 2\n");
- hashsize = 512; /* safe default */
+ int oldhashsize = hashsize;
+
+ hashsize = maketcp_hashsize(hashsize);
+ printf("%s: WARNING: TCB hash size not a power of 2, "
+ "fixed %d -> %d\n", __func__, oldhashsize, hashsize);
}
in_pcbinfo_init(&V_tcbinfo, "tcp", &V_tcb, hashsize, hashsize,
"tcp_inpcb", tcp_inpcb_init, NULL, UMA_ZONE_NOFREE,
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